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PI why normaly a 82K and a 100K from B+ to plate?


 
5/22/2000 10:35 PM
pepps
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PI why normaly a 82K and a 100K from B+ to plate?
Hello everybody  
I do not know, why there are different R from B+ to the plates of PI. Most wirings I have seen there is a 82K and a 100k.  
Thanks of help me to understand the basics.  
regards,  
pepps
 
5/22/2000 10:42 PM
Gil Ayan
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quote:
"Hello everybody  
I do not know, why there are different R from B+ to the plates of PI. Most wirings I have seen there is a 82K and a 100k.  
Thanks of help me to understand the basics.  
regards,  
pepps  
"
 
 
My understanding: has to do with the fact that one side of the PI (almost always draw -- and wired -- to the right) receives the negative feedback from the speaker jack. So that side has to work a little harder and therefore is given a larger plate load resistor so that the PI is more balanced.  
 
Gil
 
5/22/2000 10:54 PM
pepps
email

Hello Gil,  
work harder means have a higher input Voltage eff.?  
But this you can balance with the wright R between the jack and the grid, Im wrong?  
pepps
 
5/23/2000 1:15 AM
Bob
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I've had great success with 91K and 100K!  
 
Bob
 
5/23/2000 2:54 AM
Peter S
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The 82k resistor is on the inverting side because it has more gain than the no-inverting side so the resistor is a lower value to offset that. The non-inverting side with the 100k resistor actually gets a boost from the feehd back loop since the feedback is in phase with cathode. I've found that this setup works well unless you have a moderately high gain preamp and like to crank the amp all the way up. On my Marshall clone.....I changed the 100k resistor to 120k and lowered the feed back resistor a little to put a little bit more feedback into the PI.....it helps give the no-inverting side a little boost. This way my PI is a little better balanced cuz I'm slamming the output tubes very very hard with signal and if it goes off too much one tubes gets roasty toasty sooner than the other one. It's got to be a little off to get those lovely even harmonics, I just didnt want it too far off. So far it seems to be working very well.  
Peter S
 
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